I honestly couldn't stand to read every single post but I had to share what I have witnessed on multiple occasions.
Do strollers EVER fit in overhead bins? I have never seen that. I have seen families check their stroller at the gate, and when they arrive, it is brought up and they pick it up in the jet bridge. Obviously they will return the stroller to a family who has a long layover with a small child. There's no way that an airline would expect parents to just carry their child around the airport during their layover.
I suspect the GA thought he was hot stuff, decided to be difficult and was also caught up in the D0 mentality. I'm glad things got worked out, and sorry you had to deal with that crap.